1. Sex Cells and Inheritance

2. Cells- more on the nucleus
Animal and plant cells contain a nucleus.
The nucleus controls cell activities including cell division. It also contains the genetic information needed to produce a new cell.
The information is organized into units called genes.
Our genes are on chromosomes

3. Unravelling a chromosome:
                                                              
Unravelling a chromosome:
Access excellence

4. Chromosomes and Genes Chromosomes come in pairs.
Human body cells have 23 pairs of chromosomes.
This gives a diploid number of 46.
Human gametes (sperm and egg cells) contain 23 chromosomes. This is the haploid number.

5. Reproduction Revision
Pupil Activity
Complete the following sentences
Another name for sperm and egg cells is ________
These sex cells join to make one cell during __________
This cell grows into a baby by __________________ many times.
Each body cell in the baby contains ____ pairs of chromosomes.
One of the chromosomes in each pair comes from the _______, the other from the _______
gametes
fertilization
multiplying & dividing 23
mother
father

6. Human Life Cycle Diploid Zygote 46 Haploid Sperm 23 Adult 46 Haploid
Egg 23
fertilization

7. Genes
A characteristic is controlled by the two forms of a gene present in an individual.
(but the particular combinations are limited by the genetic makeup of your parents).
The different forms of a gene are called alleles. ,.

8. Genetics Buzzwords Phenotype Genotype Allele Heterozygous Homozygous
physical appearance of an organism.
Phenotype
the set of genes (alleles) that an organism possesses
Genotype
Allele
different forms of the same gene
when the two alleles are different
Heterozygous
when two alleles (gene types) are identical
Homozygous

9. Dominant
allele which controls the characteristic whenever it is present.
BB or Bb
recessive
allele whose characteristics only show up when it is present on both chromosomes bb

10. Boy or Girl?
The sex of a child is determined by specific chromosomes called X and Y chromosomes.
In humans, each male gamete may have an X or a Y chromosome, while each female gamete has an X chromosome.
Female
Body cells are XX
Male
Body cells are XY
All X
X or Y
gametes

11. Offspring: Male or female? X Y
Mother XX X
Father XY X Y
gamete
1:1 ratio male to female offspring
Offspring: Male or female? X Y XX XY
This can also be shown and combinations worked out using a Punnett square:

12. Genes and Genotypes Genotype: set of genes that an organism possesses
Each organism has two forms of the same gene
-one inherited from mother
-one inherited from father
We can say that ‘Organisms possess two alleles for each different gene’

13. Genotypes and Symbols Each allele is represented by a letter
-capital letter if the allele is dominant (A)
-lower case letter if the allele is recessive (a)
Each organism will have two letters
-1 represents the allele it receives from its mother
-1 represents the allele it receives from its father

14. Height in Pea Plants T = tall (dominant) t = short (recessive)
A pea plant can be:
TT = homozygous tall
Tt = heterozygous tall (because T is
dominant to t)
tt = homozygous short

15. Gene combinations
The simplest genetic cross involves one characteristic and is called a monohybrid cross.
In this the parents (P) are crossed (bred) with each other, and the offspring (F1 generation) observed and counted.
(Bred with) X
Parents Phenotypes
Genotypes
Gametes
Tall TT
all T
Dwarf tt
all t Tt
all tall
F1 genotype
F1 phenotype